The invention relates to a control system and method for controlling the frequency of air/fuel ratio oscillations in first and second cylinder groups of an internal combustion engine.
Known internal combustion engines generally have first and second cylinder groups that are connected to either straight pipe exhaust systems or Y-pipe exhaust systems. Both types of exhaust systems further utilize catalytic converters to reduce automotive emissions.
Known engine control systems utilize a measurement of exhaust gases from the first and second cylinder groups to maintain a predetermined air/fuel ratio in each of the first and second cylinder groups. Generally, the predetermined air/fuel ratio is stoichiometric. Further, when two-state exhaust gas oxygen sensors are utilized, a typical result is a fluctuation, or oscillation, of the exhaust air/fuel ratio about the predetermined air/fuel ratio.
With engines having Y-pipe exhaust systems, known control systems have attempted to maintain a desired phase difference between the air/fuel ratio oscillations in the first and second cylinder groups for various reasons, including to increase catalytic converter efficiency to thereby reduce emissions. In particular, known control systems have attempted to phase shift one of the air/fuel ratio oscillations either in phase or out of phase with the non-shifted air/fuel ratio oscillations.
The inventors herein have recognized a significant problem with the known control methodologies for engines having either straight pipe exhaust systems or Y-pipe exhaust systems. In particular, the known control methodologies have assumed that the frequencies of the air/fuel ratio oscillations in the first and second cylinder groups are relatively close. However, the inventors herein have determined that the frequency of the air/fuel ratio oscillations in the first and second cylinder groups may be operating at substantially different frequencies. Thus, when this occurs, merely phase shifting one of oscillations with respect to the other will not result in the desired phase difference being reached and/or maintained. Thus, the air/fuel ratio oscillations in the first and second cylinder groups move in and out of phase of one another resulting in inconsistent torque fluctuations in the engine. Further, the inconsistent torque fluctuations create undesirable vibrations and noise that can be felt and heard by occupants in an automotive vehicle.
The inventors herein have further recognized another significant problem with the known control methodologies for engines having Y-pipe exhaust systems. In particular, because the known control systems may not maintain a desired phase difference between air/fuel ratio oscillations in the first and second cylinder groups, the air/fuel ratio in combined exhaust gases from both of the cylinder groups, entering a downstream catalytic converter, may not be accurately controlled. Thus, because the air/fuel ratio entering the downstream catalytic converter may not be accurately controlled, the converter efficiency may not be optimized to thereby minimize emissions.
The invention relates to a control system and method for controlling the frequency of air/fuel ratio oscillations in first and second cylinder groups of an internal combustion engine.
A method for matching the frequency of air/fuel ratio oscillations in first and second cylinder groups of an internal combustion engine is provided. The method includes determining a first frequency of air/fuel ratio oscillations in the first cylinder group. The method further includes determining a second frequency of air/fuel ratio oscillations in the second cylinder group. Finally, the method includes adjusting the first frequency towards the second frequency responsive to a frequency difference between the first and second frequencies.
A control system for controlling first and second cylinder groups of an internal combustion engine, is provided. The control system includes a first device for determining a first frequency of air/fuel ratio oscillations in the first cylinder group. The control system further includes a second device for determining a second frequency of air/fuel ratio oscillations in the second cylinder group. The control system further includes a controller operatively connected to the first and second devices. The controller is configured to adjust the frequency of air/fuel ratio oscillations in the first cylinder group toward the frequency of air/fuel ratio oscillations in the second cylinder group responsive to a frequency difference between the first and second frequencies.
The inventive control system and method provide several advantages. In particular, the system and method adjust the frequency of air/fuel ratio oscillations in the first cylinder groups toward the frequency of the air/fuel ratio oscillations in the second cylinder group. As a result of matching the frequencies, the air/fuel ratio oscillations in both cylinder groups may be maintained at a predetermined phase difference with respect to one another. Thus, the air/fuel ratio oscillations in the first and second cylinder groups do not immediately move in and out of phase with respect to one anotherxe2x80x94which decreases and/or eliminates undesirable torque fluctuations and associated engine vibration and noise. Further, because the cylinder groups may be maintained at a predetermined phase difference with respect to one another, the operational efficiency of downstream catalytic converters can be optimally controlled to reduce engine emissions.